Variable-selectivity radio receiver



Jan. 21, 1936. 1 CRQSSLEY 2,028,534

VARIABLE SELEGTIVITY RADIORECEIVER Filed May 11, 1954 '2 Sheets-Sheet 11 l l l I I i j; 1 i: :11. i4

INVENTOR, ALF/2E0 620551.5

ATTORNEY.

Jan. 21, 1936. A, CRQSS'LIEY 2,028,534

VARIABLE SELECTIVITY RADIORECEIVER Filed May 11, 1934 2 Sheets-Sheet 2INVENTOR, ALF/2E0 CeossLsx 'QBY 4m,

ATTORNEY.

Patented Jan. 21, 1936 VARIABLE-SELECTIVITY RADIO RECEIVER AlfredCrossley, Chicago, Ill., assignor to Johnson Laboratories, Inc.,Chicago, 111., a corporation oi Illinois Application May 11, 1934,Serial No. 725,059 9 Claims. (Cl. 250-20) This invention relates broadlyto improvements in high-frequency amplifying systems, and moreparticularly to systems designed to be operated at a fixed frequency,such for example as those in the intermediate-frequency amplifiers of su-. perheterodyne receivers. In general, the selec-. tivity of thereceiver depends to a large extent upon the design of theintermediate-frequency amplifier, and it has been common practice topermanently establish the degree of selectivity at the time of thedesign and construction of the apparatus.

The object of this invention is to provide means whereby the degree ofselectivity of the receiver may be varied at the will of the operator.An-

other object of the invention is to provide means whereby the overallfidelity or tonal reproducing properties of the receiver ,may beadjusted to suit the requirements of the person operating the receiver.

A further object of this invention is to provide means for obtaining anyof the above-mentioned qualities by v rious coupling systems with whichare associated suitable mechanical means for inmatically securing adesired adjustment of selectivity or fidelity for each of a plurality ofchannel positions of the station-selecting means of the receiver.

Additionally, it is an object of this invention to provide adjustablecoupling means for varying the coupling from substantially zero to anypredetermined value, the upper limit of coupling being independent ofand not subject to control by the operator.

At the present time, radio broadcast stations -transmit on assignedfrequencies ten kilocycles apart. The resultant ten kilocycle channelwidth permits the transmission of side-band frequencies up to 5000cycles. The ideal receiver for operation under these conditions wouldhave a rectangular selectivity curve" (response vs. frequency) just tenkilocycles wide. capable of receiving everything being transmitted in agiven channel and of excluding all other signals.

In practice, howevenit is not possible to obtain a straight-sidedselectivity curve, and hence some sacrifice of the higher side-bandfrequencies must be made to insure satisfactory separation 01' broadcaststations transmitting: 'on adjacent channels. The extent to which thiscompromise between selectivity and fidelity must be carried is largelydeterminedby local conditions, includdicating the adjustment prevailingat any time. Still another object is to provide means for auto-.

It would be ing the requirements of the person operating the receivenandthe relative field strengths of thevarious broadcast stations. Hence itis practically impossible to so design a radio receiver that it willgive entirely satisfactory receptionin 5 widely varying circumstances.For example, a receiver having sufiicient selectivity to permit ofsatisfactory reception from a distant broadcast station operating on achannel adjacent to that of a strong local station would attenuate the10 higher side-band (audible) frequencies so seriously that it could notgive substantially faithful reproduction from a near-by stationoperating in a channel somewhat removed from other powerful stations. 15

The means disclosed in thisinvention permit the degree of selectivity tobe readily varied to meet the requirements of any location or the wishesof any operator, within wide limits. Furthermore, the. limits may beaccurately predeb termined and the setting definitely indicated, or evenautomatically established for certain channels. It will be understoodthat this selectivity adjustment will also act as an adjustment of theoverall fidelity of the receiver, since the amount of side-bandattenuation and hence the relative strength of the higher audiblefrequencies will depend upon its setting. Thus the operator of thereceiver'rather than the original designer is the final judge regardingthe most satisfactory compromise between selectivity and fidelity forany given conditions.

The objects of this invention are attained by varying the amount ofcoupling between successive stages in the intermediate-frequencyamplifier of the receiver. This coupling may be entirelyelectromagnetic, entirely electrostatic; or electromagnetic andelectrostatic combined. The coupling device usually consists of firstand second windings, and'in some cases includes aux- 0 iliarycapacitance to provide electrostatic coupling. Even without thisauxiliary capacitance, there is usually a small amount of electrostaticcoupling due to the capacitance between the highpotential leads to thecoils.

Qne embodiment of this invention utilizes a coupling device having asmall fixed amount of electrostatic coupling, provision being made tovary the electromagnetic coupling by changing the relative positions ofthe first and second coils. In another embodiment, the'coils are sopositioned with respect to each other that there is substantially zeroelectromagnetic coupling. The electrostatic coupling in this case isvaried by changing the capacitance of a condenser connected between thehigh-potential terminals of the two windings. In a modified form of thisembodiment, the capacitive coupling means may be associated with thelow-potential terminals of the two windings.

Preferred embodiments of this invention utilize coils withferro-magnetic cores. These cores consist of finely-divided individuallyinsulated iron particles compressed with a binding material to make acore body. Cores of this type, suitable for use athigh frequencies, aredisclosed in British Patents Nos. 366,475 and 403,368, and have recentlybeen described in numerous publications in the United States and abroad.

The inductances are preferably designed in acthereof. A lesser degree ofefliciency will be obtained, however, in the general performance of thesystem.

For a complete understandingof the invention,

\ the following description should be read in connection with .theaccompanying drawings, in which- Figure 1 is a cross-sectional sideelevation of one desirable embodiment of the invention;

Figure 2 is a front elevation of a manual control device which may beused in conjunction with the invention; I

Figure 3 is a cross-sectional side elevation of another embodiment ofthe invention;

Figure 4 is a wiring diagram showing embodiment of Figure 1, or asimilar embodiment, is to be connected;

Figure 5 is a wiring diagram showing how the embodiment of Figure 3, ora similar embodiment, is to be connected; t

Figure dis a schematic front elevation showing one form of the inventionarranged for automatic operation in conjunction with the stationselecting means of the receiver; and

Figure 7 is a view of part of the contact mem ber of the automaticdevice indicated in Figure 6, taken on the line 1-1 of Figure 6.

Referring to Figure 1, the embodiment shown varies the electromagneticcoupling between the coils in each of the two interstage couplingdevices by moving one coil relatively to the other. A shaft I issupported by the l-l-shaped coupling device frame 2. Movable coil 3 issupported between sections of the shaft l by means of insulating members4, which are provided with studs fitting into the tubular core of coil3, these studs being held in place by any suitable cement. The members 4are provided with shoulders 5 to provide a thrust bearing against frame2. The coil 3 is so mounted that its axis intersects the axis of shaft iby an angle 0, which is of the correct value to give the desired degreeof maximum coupling when the coil 3 is so positioned that its axis liesin a vertical plane also containing the axis of the shaft l.

The fixed coil 6 is mounted with its axis vertical, its tubular corebeing suitably cemented over a stud extending vertically from thecrosshow the member of the .frame 2. The shaft l passe through a hole Iin the front panel 8 of the receiver, and may be rotated manually bymeans of knob 9. Its position is indicated by means of an escutcheon l0,suitably attached to the panel 8. Each coupling device is provided. witha shield l I, having a removable cover l2, and attached to sub-panel I3by. means of rivets ll or by other suitable means. The control isarranged to operate the two devices simultaneously by means of thecoupling l5. Additional coupling devices may be added and will beoperated by the coupling I511.

This method has the advantage. of providing a very gradual. adjustmentof the. coupling, and an adjustment which is not disturbed by vibration.It is to be understood that modified forms for obtaining a change in thedegree of coupling which may suggest themselves to those skilled in theart fall within the scope of this invention, the above-describedembodiment'representing a preferred form.

Figure 2 shows one form of escutcheon which may be used to indicate thedegree of selectivity for which the adjustment is set. In certainapplications, the escutcheon may preferably bear the words local anddistance" instead of numbers, the local position corresponding to theminimum selectivity setting and the distance posi- =tion to the maximumselectivity setting. Other variations will readily occur to thoseskilled in the art, according to the particular application of thedevice.

In the embodiment shown in Figure 3, the coils 3 and 6 are so placedwith respect to each other that there is substantially zeroelectromagnetic coupling between them. Electrostatic coupling is used inthis embodiment of the invention, and it is obtained by connecting anadjustable condenser between the high-potential terminals of the firstand second windings. Condenser plate I6 is secured to a squareinsulating rod H by any suitable means, such as'a set screw inserted ina collar attached to plate IS. The fixed condenser plate I8 is securedto the top H of the shielding can II by means of an insulating bracket20. The rod H has attached to it a threaded metal rod 2| which engagesthe threaded inside portion 22 of the knob 23. Square holes in theshielding can ll prevent the rod i! from rotating when the knob 23 isturned. Front panel 8 or a suitable bracket attached to the sub-panel i3is located between the shoulder of threaded sleeve 22 and thrust disc24, thus preventing axial movement of the rotating parts. A set-screwcollar 25 is provided to limit the motion of plate I 6 toward plate I8,and hence the maximum amount of electrostatic coupling may be definitelyset. Due to the screw movement, it will be necessary to provide agreater arc of rotation for the knob 23 and consequently the escutcheonl0 may be of the full circular type instead of the arc or segmentconstruction shown in Figure 2. The condenser plates l5 and i8 areconnected by leads 26 to the high-potential terminals of coils 6 and 3,respectively. The shield ll associated with this unit is secured to thesubpanel l3 by the conventional rivets l4.

Figure 4 shows the connections for a system employing variableelectromagnetic coupling. The antenna coil-2'! is coupled to theradio-frequency coil 28, which is tuned to resonance by variablecondenser 29 and connected in the control-grid circuit of the pentagridconverter 30. To simplify the diagram and explanation, I have omittedthe oscillating circuit which is assolciated with the pentagridconverter to obtain an intermediate frequency in the well-knownsuperheterodyne manner. The plate circuit of the pentagrid converterincludes the first winding 3| of an intermediate-frequency couplingdevice,

the winding 3| being tuned by adjustable condenser 32 and variablycoupled electromagnetically to the second winding 33, which is tunedamplifier and output system. The plate circuits or the pentagridconverter 33 and of the amplifier tube 3.3 have associated with themby-pass condensers 39 which substantially prevent the flow ofintermediate-frequency current through the plate-voltage supply source.

Figure shows an arrangementusing the identical antenna input tuningsystem and pentagrid converter together with the first winding of thefirst intermediate-frequency coupling dethe sake of simplicity. Thecondenser 40 is shown connected between the high-potential terminals ofthe first and second windings, but electrostatic coupling may also beobtainedby the use of suitable condensers associated with thelow-potential side of the coils. The coupling condenser in that casewill have much greater capacitance, and hence the preferred embodimentis that shown in the figure.

In Figure 6 isshown one arrangement for automatically changing theselectivity of the receiver when the station selector has certainpredetermined settings. For example, it might be desirable to obtain thebest possible fidelity from three or four nearby stations, and yet havethe full selectivity of the receiver restored when it is tuned to allother frequencies. A rotary insulating disc 4| is mounted on the stationselector or dial shaft 42, having at one end thereof the conventionaldial 42b, and at its periphery carries several contacts 43 which, at 43a(Figure 7), extend over and are adjustable around the periphery of thedisc. The contacts 43 are conneeded by means of suitable springs 43b tothe shaft 42, which in turn is connected to a contact spring 42a. Acontact spring 44- is arranged to make point contact, on occasion, withany one of the contacts 43, thus completing a circuit through thesolenoid 45 and the source of potential 46. Each contact 43 is adjustedto correspond with the indicated dial position of each individualstation on which best fidelity is desired. When current flows throughthe solenoid 45, its armature 41 is attracted. This motion istransmitted through link 48 to arm 48, and by means of link 50 and crank5|, the shaft of the variable selectivity device is oscillated. When thecontact is broken and current ceases to flow thru the solenoid 45, theshaft I is restored to the maximum selectivity position by means ofspring 52. Hence it will be seen that the system is normally in thecondition of maxicontact 43 secured to it by the set screw 53.

. 3 mum selectivity, but at'predetermined settings of the stationselector it is automatically adjusted junction with automatic operation.It is to be understood that other methods for obtaining automaticoperation and methods for combined manual'and automatic operation willreadily occur to those skilled in the art, and may be employed withoutexceeding the scope of this invention.

The details of the movable contact 43 are shown in Figure '7. Thisfigure is a sectional view of a portion of the insulating disc 4| withthe As shown in Figure 6, the insulating disc 4| has a facial groove 4|awhich receives the inner end of the set screw. By loosening the screw53, the contact 43 may be moved along the periphery of the disc 4| tothe desired position. When the set screw is tightened, the. terminal 43aof the contact 43 presses against-the disc 4| and holds the contact 43in that position.

In addition to the operating advantages which are obtained by the use ofvariable coupling between the first and second windings of the couplingdevices, the adjustable feature permits much more rapid and accurateinitial alignment of the fixed-frequency amplifier at the time ofmanufacture. By setting the coupling at the minimum coupling position,each tuned circuit maybe adjusted to resonance with practically nointeraction and with this initial adjustment any increase in couplingproduces a broadening of the nose of the selectivity curve with noirregular sides or humps. This tuning operation is a simple one and onlywith this system can such a simple method be employed to provide anydesired degree of coupling. In the conventional type of coupling devicethe coupling is fixed which, where overcoupling is desired, makes tuningdiificult due to reaction between the coils, and resort has to be madeto special oscillographic apparatus to tune such circuits.

The fact that I use variable electromagnetic coupling having fixedposition of terminal'or lead wires together with novel means forrotating the coil such that no variation in capacitance between coils ispossible makes it practical to obtain this remarkable result. In thecase where variable capacitive coupling is used, the desired result isobtained because it is possible to adjust the electromagnetic couplingto zero. This zero coupling is obtained by positioning the horizon talcore so that its axis is substantially at right angles to the axis ofthe lower core, as shown in Figure 3.

Having thus described my invention, what I claim is: w

1. A fixed-frequency amplifier including pairs of coupled resonantcircuits, each of said pairs comprising two ferro-magnetic-coredinductors, one inductor in each of said pairs being rotatable andmounted at an oblique angle to its axis of rotation, and means forrotating said rotatable 2. A fixed-frequency amplifier including pairsof coupled resonant circuits, each of said pairs comprising one fixedand one rotatable ferromagnetic-cored inductor, said rotatable inductorsbeing mounted with their axes at an oblique angle to the axis ofrotation, and means for rotating said rotatable inductors in unison tovary the coupling between said coupled resonant circuits, l

f3. A fixed-frequency amplifier including pairs of coupled resonantcircuits, each of said pairs comprising one fixed and one rotatableferromagnetic-cored inductor, said rotatable inductors being mountedwith their axesat an oblique angle to the axis of rotation, said obliqueangle being chosen to determine the maximum degree of coupling in eachof said pairs of coupled circuits, and means for rotating said rotatableinductors in unison to vary the coupling between said coupled resonantcircuits.

4. A fixed-frequency amplifier including pairs of coupled resonantcircuits, each of said pairs comprising one fixed and one rotatableferromagneticfcored inductor, said rotatable inductors being mounted ata chosen oblique angle to j theirvcommon axis of rotation, said commonaxis of rotation being at right angles to the axes of said fixedinductors whereby said rotatable inductors may-be rotated to a positionof substantially zero electromagnetic coupling to said fixed inductors,said oblique angle determining the maximum degree of coupling betweensaid rotatable and said'fixed inductors.

5. A radio v receiver having a fixed-frequency amplifier includingcoupling devices comprising first and second windings, each of saidwindings having a term-magnetic core, and two of said windings beingeccentrically mounted for varying the selectivity of said receiver byrotating, in

unison, said eccentrically mounted windings and cores rela'tively totheir respective cooperating windings. I

6. A radio receiver, having a fixed-frequency amplifier includingcoupling devices comprising -first and second windings, each of saidwindings having a term-magnetic core, and two of said windings beingeccentrically mounted for simultaneously varying the selectivity and thefidelity of said receiver by rotating, in unison, saideccentrically-mounted windings and cores relatively to their respectivecooperating windings.

7. A radio receiver having a fixed-frequency amplifier includingcoupling devices comprising first and second windings, each of saidwindings having a ferro-magnetic core, said receiver including means forvarying the selectivity of said receiver by rotation in unison 01 atleast two of said windings and cores with respect to their respectivecooperating windings and cores, whereby the degree of electromagneticcoupling therebetween is varied.

8. A radio receiver having a fixed-frequency amplifier includingcoupling devices comprising first and second windings, each of saidwindings having a term-magnetic core, said receiver i ncluding means forsimultaneously varyirig the selectivity and the fidelity of saidreceiver by rotation of one winding and core in at least two of saidcoupling devices with respect to the other winding and core, whereby thedegree of electromagnetic coupling therebetween is varied from acondition of loose coupling to a condition of somewhat greater thanoptimum coupling.

9. A radio receiver having a fixed-frequency amplifying circuit and avariable coupling in said circuit, combined with an electrical switchingmechanism for eifectuating desired selectivity characteristics or saidcircuit when receiving broadcast signals of different, frequencies, saidswitching mechanism including an electrical circuit comprising arevoluble insulating disc carrying an adjustablecontact, a fixed contactwith which said adjustable contact may engage,

V a solenoid, a source of voltage Ior energizing said solenoid when saidfixed and said adjustable contact are engaged, and a train of mechanismsactuated by the armature of said solenoid for adjusting said variablecoupling ALFRED CROSSLEY.

